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  • Blues Junior trace be gone

    I just got this in , no sound , powers up , all tubes are lit , slight hum from the speaker . First suspect the cheesy input jack , get access to the back of the board surprise trace taken out by the output transformer mounting screw ?. After cleaning it off a bit , I can't quite tell if there were 2 traces side by side ? It's a silver panel, so I don't believe it to be a Junior III. Always appreciate your input

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    Fender-Blues-Junior-Schematic highlight.pdf
    https://www.thetubestore.com/lib/the...-Schematic.pdf

    If I'm following the schematic correct I'm thinking I can run jumpers as such , yes? D12 R34 R36 all survived
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    Last edited by shortcircuit; 06-18-2019, 05:03 PM.
    If you don't know where your going any road'll take you there : George Harrison

  • #2
    Originally posted by shortcircuit View Post
    I just got this in , no sound , powers up , all tubes are lit , slight hum from the speaker . First suspect the cheesy input jack , get access to the back of the board surprise trace taken out by the output transformer mounting screw ?. After cleaning it off a bit , I can't quite tell if there were 2 traces side by side ? It's a silver panel, so I don't believe it to be a Junior III. Always appreciate your input

    [ATTACH=CONFIG]54026[/ATTACH][ATTACH=CONFIG]54027[/ATTACH]
    [ATTACH]54028[/ATTACH]
    https://www.thetubestore.com/lib/the...-Schematic.pdf

    If I'm following the schematic correct I'm thinking I can run jumpers as such , yes? D12 R34 R36 all survived
    [ATTACH=CONFIG]54036[/ATTACH]
    Yes, there are two traces. I've shown them in RED, adding them to your photo below:

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    Logic is an organized way of going wrong with confidence

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    • #3
      Thank You nevetslab !!!!
      If you don't know where your going any road'll take you there : George Harrison

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      • #4
        Do grind out any of the charred circuit board before adding the jumpers. Once burnt that circuit board can become conductive.
        "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

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        • #5
          Originally posted by The Dude View Post
          Do grind out any of the charred circuit board before adding the jumpers. Once burnt that circuit board can become conductive.
          Thanks Dude , I was going to ask what others would do to deactivate the remains
          If you don't know where your going any road'll take you there : George Harrison

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          • #6
            I usually just scrape/cut it away with an x-acto knife if it's not too bad. Sometimes it requires a dremel tool. Get it down to where you no longer see charring.
            "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

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            • #7
              Originally posted by shortcircuit View Post
              Thanks Dude , I was going to ask what others would do to deactivate the remains
              A recent PCB trace burn repair done on an Aguilar DB 751:

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              After having scraped away all of the chared remains, which took going down a full level of the fiberglass layer, I had coated the area with Corona Dope, two coatings, just to put a seal on it. That's mostly for areas that are carrying high voltage. I haven't looked at the Blues Jr to see just where this damage is.
              Logic is an organized way of going wrong with confidence

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              • #8
                Originally posted by The Dude View Post
                I usually just scrape/cut it away with an x-acto knife if it's not too bad. Sometimes it requires a dremel tool. Get it down to where you no longer see charring.
                Do you use any sealer of any kind after ?? I see nevetslab mention the Corona
                If you don't know where your going any road'll take you there : George Harrison

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                • #9
                  I'm not positive what those traces are for, but I see a brown and blue wire nearby. Maybe OT leads? If so, they will have B+ on them. A little Corona Dope wouldn't hurt. That said, if you clean the burnt board out well, I don't think it's necessary. What's left won't be any more conductive than it was to start with. And, it goes without saying, don't forget to do something about the screw that started the whole mess. (I know,......Mr. Obvious)
                  "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

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                  • #10
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                    Be careful with the contamination in that area. From left to right:
                    D12 - diode between EL84 plate and ground.
                    R34 - input grid resistor
                    R36 - screen grid resistor
                    R32/31 - bias feed resistors

                    Requires total isolation between these components. The corresponding EL84 could have also some problem...

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                    • #11
                      Originally posted by Pedro Vecino View Post
                      [ATTACH=CONFIG]54042[/ATTACH]

                      Be careful with the contamination in that area. From left to right:
                      D12 - diode between EL84 plate and ground.
                      R34 - input grid resistor
                      R36 - screen grid resistor
                      R32/31 - bias feed resistors

                      Requires total isolation between these components. The corresponding EL84 could have also some problem...
                      Yes critical area , that's why I'm looking for a sealer, but I only need a fingernail polish bottle not a quart /and have found but shipping. V5 El84 tested great (Russian Groove tube) , socket pads look iffy , so maybe trans screw was just an easy blame at first.
                      Last edited by shortcircuit; 06-19-2019, 12:48 AM.
                      If you don't know where your going any road'll take you there : George Harrison

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                      • #12
                        Originally posted by shortcircuit View Post
                        Yes critical area , that's why I'm looking for a sealer, but I only need a fingernail polish bottle not a quart /and have found but shipping.
                        You might find 'liquid tape' at a hardware store. It's not as good and may take a couple layers. The important spec. is dielectric strength in V/mil, corona dope is around 4000, liquid tape more like 2000 or less.
                        Check to be sure, some of them are just basically for waterproofing.
                        Originally posted by Enzo
                        I have a sign in my shop that says, "Never think up reasons not to check something."


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                        • #13
                          I've had to drill out bc sections of fried boards.

                          After cleaning check for any stray resistance before coating in your substance of choice.

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                          • #14
                            Originally posted by g1 View Post
                            You might find 'liquid tape' at a hardware store. It's not as good and may take a couple layers. The important spec. is dielectric strength in V/mil, corona dope is around 4000, liquid tape more like 2000 or less.
                            Check to be sure, some of them are just basically for waterproofing.
                            Thanks for the info G1 , because of where this is on the board, I'll opt for the Corona.
                            If you don't know where your going any road'll take you there : George Harrison

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                            • #15
                              Corona Dope source

                              Originally posted by shortcircuit View Post
                              Thanks for the info G1 , because of where this is on the board, I'll opt for the Corona.
                              The source for the MG Chemicals Super Corona Dope P/N 4226-55ML is Mouser Electronics, their P/N 590-4226-55ML @ $11.06 55mL bottle.
                              Logic is an organized way of going wrong with confidence

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